1. Field of the Invention
The present invention relates to a multi-part piston for an internal combustion engine, having an upper piston part and a lower piston part. The upper piston part and the lower piston part each have an inner and an outer support element, which elements delimit an outer circumferential cooling channel and an inner cooling chamber. The present invention furthermore relates to a method for the production of such a piston.
2. The Prior Art
Multi-part pistons have the great advantage that the upper piston part and the lower piston part can consist of different materials. The upper piston part is generally produced from a particularly wear-resistant material, particularly one that is heat-resistant, but relatively heavy, while the lower piston part is generally produced from a light-metal material that is less wear-resistant, in order to save weight. Furthermore, the outer circumferential cooling channel and the inner cooling chamber are connected with one another by bores that are made in the inner support elements. They serve as overflow bores for the cooling oil, which can pass from the outer cooling channel into the inner cooling chamber, and vice versa, on this path, and can flow away in the direction of the piston crown.
In this regard, the connection between the upper piston part and lower piston part causes problems, as is explained in detail in European Patent No. EP 1 483 493 B1. The upper piston part and the lower piston part can be welded to one another, for example, or screwed together with one another. Each of these connection techniques has specific advantages and disadvantages. The preferred joining method is friction welding, particularly if the upper piston part and/or the lower piston part are produced from a steel material. However, friction welding has the disadvantage that great burr formation accompanies the joining process. This has the result that the bores that connect the outer circumferential cooling channel and the inner cooling chamber with one another can only be introduced after joining. Otherwise, there is the risk that bores made before joining will be partially or completely closed up during the friction-welding process, as the result of the strong burr formation. However, introducing the bores afterwards is very complicated.